Method for monitoring operating parameters of a rechargeable power supply

ABSTRACT

A method for monitoring various parameters and conditions of a rechargeable battery to accurately determine the remaining charge level of the rechargeable battery, and includes using a temperature sensor to monitor the temperature of the rechargeable battery. The potential level of the rechargeable battery is monitored with a voltage meter coupled to the rechargeable battery. The current flow into and out of the rechargeable battery is monitored with current meter coupled to the rechargeable battery. A current accumulator coupled to the current meter is used to accumulate the net total of current flow, and an oscillatory circuit is used to generate a timing signal to time selected functions.

FIELD OF THE INVENTION

[0001] This invention relates to rechargeable batteries, and moreparticularly, but not by way of limitation, to method for monitoringvarious operating parameters of a battery cell within a rechargeablebattery pack, and using these parameters to accurately determine theremaining operating life of the rechargeable battery pack.

BACKGROUND OF THE INVENTION

[0002] Many portable electronic systems, such as laptop computers andcellular phones, utilize rechargeable battery packs to receive theirpower. Such battery packs have the advantage that they are portable,relatively weight efficient, and can be charged and discharged manytimes. However, due to certain characteristics of existing rechargeablebattery packs, an accurate indication of the remaining charge is verydifficult to determine.

[0003] As can be appreciated, it is very desirable to be able toaccurately determine the remaining operating life of a rechargeablebattery pack used in a system such as a laptop computer. This enables auser to get maximum use out of the rechargeable battery pack. This isespecially critical when the remaining energy of the rechargeablebattery pack falls below the operating threshold of the computer. A userwould ideally want to be able to safely shut down the computer priorthereto, thereby preventing any potential loss of information.

[0004] The amount of the charge flowing into and out of the rechargeablebattery pack during charging and discharging are parameters that can bemonitored and used to calculate the remaining charge of a rechargeablebattery. As can be further appreciated, the more accurately and reliablythis information is measured and accumulated, the more accurate thecalculation of the remaining charge of the rechargeable battery.

[0005] In addition to the discharge that occurs during regular use of arechargeable battery pack, a rechargeable battery pack will also have acertain amount of self-discharge when not in use. This self-discharge isvery difficult to account for when calculating the remaining charge ofthe rechargeable battery. In existing rechargeable battery packs, theamount of time the rechargeable battery pack is not being used is verydifficult to determine. Additionally, the amount of self-discharge of arechargeable battery will fluctuate with varying temperatures. As can beappreciated, a problem with existing rechargeable battery packs is thatthey do not take into account the self-discharge of the battery, nor dothey take into account the varying temperatures when calculating theremaining charge of the rechargeable battery.

[0006] Therefore, there is a need for a method to accurately andreliably determine the remaining operating life of a rechargeablebattery.

SUMMARY OF THE INVENTION

[0007] The present invention overcomes the above identified problems aswell as other shortcomings and deficiencies of existing technologies byproviding a method for monitoring the temperature of the rechargeablebattery, measuring the current flow into and out of the rechargeablebattery, accumulating the net total of current flow into and out of therechargeable battery, and generating timestamps from a highly accuratetimekeeper that can be used to indicate the time of the end of thecharging for the rechargeable battery, and used to indicate the time ofthe disconnect of the rechargeable battery from a system.

[0008] The present invention further provides a method, using a lowpowered electronic device, for monitoring the operating conditions of arechargeable battery. A temperature sensor is used for monitoring thetemperature of the rechargeable battery. A voltage meter is coupled tothe rechargeable battery and is used for measuring the potential levelof the rechargeable battery. A one wire interface is used forcommunicating to a used, information corresponding to the monitoredparameters of the rechargeable battery. A current meter which is coupledto the rechargeable battery is used for measuring the flow of currentinto and out of the rechargeable battery. A current accumulator which iscoupled to the current meter, is used for accumulating the net total ofcurrent flow, and a highly accurate timekeeper is used for generating atiming signal to time selected functions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] A more complete understanding of the present invention may be hadby reference to the following Detailed Description when taken inconjunction with the accompanying Drawings wherein:

[0010]FIG. 1 is a diagram illustrating a rechargeable battery utilizingthe present invention; and

[0011]FIG. 2 is a graph illustrating the activity of the currentaccumulators of the present invention over a sample charge/dischargecycle.

DETAILED DESCRIPTION

[0012] With reference now to FIG. 1, there is illustrated a schematicdiagram illustrating an exemplary embodiment of a system 100 utilizingthe present invention. In this exemplary embodiment system 100 is arechargeable battery pack and includes battery monitoring circuitry 102with some peripheral circuitry connected thereto.

[0013] The Dallas Semiconductor DS2437 Smart Battery Monitor illustratesan exemplary embodiment of an electronic device utilizing batterymonitoring circuitry 102, the data sheet of which is incorporated hereinby reference.

[0014] As depicted in FIG. 1, battery monitoring circuitry 102 includesa 64-Bit serial number and one-wire control circuitry 110; disconnectsense circuitry 112; temperature sensor 114; an oscillator, e.g.oscillatory circuitry 116; a voltage analog-to-digital converter 118; acurrent analog-to-digital converter 120; scratchpad memories 122, 124,126 and 128, each having an 8-bit CRC; a temperature register 130;battery voltage register 132; battery current register 134; clockregister 136; disconnect registers 138; non-volatile memory 140; anintegrated current accumulator 142; a charge current accumulator 144; adischarge current accumulator 146; and control logical circuitry 152.

[0015] As further depicted in FIG. 1, some of the peripheral circuitryconnected to battery monitoring circuitry 102 includes a crystal 150,and rechargeable battery cells or rechargeable batteries 154.

[0016] The use of the 64-bit serial number and single-wire control 110allows the tagging of rechargeable battery pack 100 with a unique serialnumber such that multiple battery pack monitors could exist and beutilized on the same single-wire data bus, i.e. several battery packscould be charged/monitored by the same host system. Additionally, in anexemplary embodiment, temperature sensor 114 eliminates the need forthermistors in the battery pack through the utilization of adirect-to-digital temperature sensor. Voltage analog-to-digitalconverter 118 and current analog-to-digital converter 120 measure therechargeable battery's voltage and current, respectively.Analog-to-digital converters 118 and 120 permit the monitoring ofbattery cells 154 to determine the end-of-charge and theend-of-discharge thereof. Integrated current accumulator 142 keeps trackof the remaining capacity of battery cells 154, while the chargingcurrent accumulator 144 keeps a running total of all charge havingflowed into battery cells 154, and the discharging current accumulator146 keeps a running total of all charge having flowed out of batterycells 154. The current measurements of the current analog-to-digitalconverter 120 and the values stored in 142, 144 and 146 currentaccumulators can be utilized to calculate the capacity remaining inbattery cells 154. The data generated by oscillator 116, i.e. clockdata, is stored in clock register 136, and can be used to calculatebattery self-discharge or time-related charge termination limits.

[0017] Battery monitoring circuitry 102 can receive power over aone-wire data bus connected to input pin DQ, which is connected to theone-wire control circuit 110. Battery monitoring circuitry 102 “steals”power whenever the signal at the DQ I/O is high; this is known as“parasite” power. The advantage of parasite power is that serial numbersstored in memory can be read in the absence of normal power, such aswhen the battery cells 154 are completely discharged.

[0018] Still referring to FIG. 1, temperature sensor 114 is used tomeasure the temperature of rechargeable battery pack 100, with the datacorresponding to the sensed temperature of rechargeable battery pack 100being stored in temperature register 130. Generally a temperaturereading is taken at selected intervals, determined by oscillator 116,wherein the data corresponding to the sensed temperature is passed totemperature register 130 by control logic circuitry 152. The data canthen be accessed by a user through DQ input/output over a one-wire databus controlled by one-wire control circuitry 110. In one exemplaryembodiment, good results have been achieved by using a temperaturesensor wherein the data corresponding to the sensed temperature isconverted by the temperature sensor from analog to digital, such thatthe temperature data can be transmitted digitally, directly from thebattery monitor over the one-wire data bus by one-wire control 110.

[0019] Although the exemplary embodiment of the present invention asdescribed herein is depicted as utilizing one-wire data bus technology,it is contemplated that the present invention is not necessarily limitedto this technology, but rather can be practiced with virtually any typeof data bus technology, such as, but not by way of limitation, two wiredata bus architecture and three wire data bus architecture.

[0020] Still referring to FIG. 1, voltage analog-to-digital converter118 is coupled to battery cells 154 through the VDD port. Voltageanalog-to-digital converter 118 measures and determines the voltage ofbattery cells 154. Voltage analog-to-digital converter 118 performs ananalog-to-digital conversion when instructed to do so by a commandreceived from the host at the DQ input/output. The result of the voltagemeasurement is placed in battery voltage register 132, which is atwo-byte register. This information is accessible by external devicesthrough DQ I/O interface.

[0021] Still referring to FIG. 1, battery monitoring circuitry 102includes current analog-to-digital converter 120 which is used tomonitor current flow into and out of the battery cells 154. In oneexemplary embodiment, current analog-to-digital converter 120 includes asigma-delta analog-to-digital converter that measures the current flowinto and out of battery cells 154. This is performed at a rate of 32measurements/sec as clocked by oscillator circuit 116 with no usercommand required to initiate the current flow measurements. Current ismeasured into and out of battery cells 154 through the VSENS pins, withthe voltage from the VSENS+ pin to the VSENS− pin equal to the voltageacross capacitor C_(F). Good results have been achieved by connectingcurrent analog-to-digital converter 120 to a filter (resistor, R_(F) andcapacitor, C_(F)) which serves to average the voltage across R_(SENS)(which reflects the current into or out battery cells 154). This filteris configured to capture the effect of current spikes that may occurduring operation. By averaging current spikes, current accumulators 142,144 and 146 can more accurately reflect the total charge which has goneinto and out of the battery. In one exemplary embodiment, the current ispresented as a 9-bit signed number with 10-bit resolution, with the lastcompleted measurement written to battery current register 134.

[0022] Still referring to FIG. 1, there are three current accumulators,an integrated current accumulator (ICA) 142, a charging currentaccumulator (CCA) 144, and a discharging current accumulator (DCA) 146,with each accumulator being driven by oscillator 116. Each accumulatorfurther includes a register associated therewith. ICA 142 maintains anet accumulated total of current flowing into and out of battery cells154, whereby a reading taken from the register of ICA 142 gives anindication of the remaining capacity of battery cells 154, and can beused in performing gas gauge functions.

[0023] CCA 144 is used to accumulate battery charging (positive)current, while DCA 146 is used to accumulate discharging (negative)current. The information generated by CCA 144 and DCA 146 is used todetermine the end of battery life of the battery cells 154, based on thetotal charge/discharge current over the lifetime of the battery cells154. The current measured by current analog-to-digital converter 120yields a result which is the average of the current measured over theselect time interval clocked by oscillator 116 (such as every 31.25 ms).This measured current is then used to increment or decrement theregister of ICA 142, increment the register of CCA 144 (if current ispositive), and increment the register of DCA 146 (if the current isnegative).

[0024] In an exemplary embodiment, ICA 142 is a 0.01C resolution, 8-bitvolatile binary counter driven by oscillator 116 and represents theamount of capacity remaining in battery cells 154. The amount ofcapacity remaining in battery cells 154 is measured in terms of the fullcapacity (1C) of the battery cells normalized to a count of 100₁₀. Thus,an ICA count of 100₁₀ represents IC of charge, i.e. 100% capacity orfully charged. An ICA count of 0 represents 0% capacity, i.e. fullydischarged. In this exemplary embodiment, ICA 142 will count up to 255₁₀(2.55C), since charging of battery cells 154 typically provides to thebattery cell more than its capacity. When this occurs, ICA 142 can bereset to a count of 100₁₀ when charging is complete, to indicate thatthe battery cells are at 100% of capacity, and to further ensure thatlater gas gauge measurements are accurate.

[0025] Still referring to FIG. 1, in this exemplary embodiment of system100, CCA 144 is a two-byte, 0.32C resolution, non-volatile read/writecounter which represents the total charging current battery cells 154have encountered in their lifetime. CCA 144 is only updated when currentthrough R_(SENS) is positive and battery cells 154 are being charged.The non-volatility of the register of CCA 144 will allow thisinformation to accumulate over the lifetime of battery cells 154 andwill not be lost when battery cells 154 become discharged.

[0026] DCA 146 is a two-byte, 0.32C resolution, non-volatile counterwhich represents the total discharging current battery cells 154 haveencountered over their lifetime. DCA 146 is only updated when currentthrough R_(SENS) is negative and battery cells 154 are being discharged.As with the register of CCA 144, the non-volatility of the register ofDCA 146 allows this information to accumulate over the lifetime ofbattery cells 154 and will not be lost when battery cells 154 becomedischarged. In normal operation, when battery cells 154 become fullydischarged, the value of the register of ICA 142 reaches zero, while thevalues of the registers of CCA 144 and DCA 146 are maintained.

[0027] Continuing to refer to FIG. 1, oscillator circuit 116 and crystal150 together form a highly accurate clock used to generate a timingsignal which is used for the timebase of the timekeeping functions. Inoperation, oscillator circuit 116 is driven by crystal 150 and operatesas a clock with a four-byte binary counter with a 1 -second resolution.The four bytes are a count of seconds. The timekeeping functions aredouble buffered, allowing a user to read time without the data changingwhile it is being read. This is accomplished by taking a “snapshot” ofthe counter data and transferring it to clock register 136, which theuser accesses.

[0028] As described herein above, the three current accumulators operateat select time intervals as clocked by the timing signal generated byoscillator circuit 116 and crystal 150. Another of the functionsutilizing the timing signal generated by oscillator circuit 116 andcrystal 150 is a disconnect timestamp. When disconnect sense circuitry112 senses that the signal at DQ pin has been low for more than one fullsecond, indicating that rechargeable battery pack 100 has been removedfrom a system, a disconnect timestamp representing disconnect time iswritten into the disconnect register 138. Upon replacement of batterypack 100 into the system, the determination of how long the battery hasbeen in storage can be made, thereby facilitating self-dischargecorrections to the remaining battery capacity.

[0029] Still another function utilizing the timing signal generated byoscillator circuit 116 is an end-of-charge timestamp. During thecharging of battery cells 154, when current changes direction, asdetected by current analog-to-digital converter 120, the charging ofbattery cells 154 is finished. When this occurs, an end-of-chargetimestamp is written to a register. This timestamp further allows theuser to calculate the amount of time battery pack 100 has been in adischarge or storage state, further facilitating self-dischargecalculations.

[0030] The above described timestamps, among other things, are used tocalculate the amount of self-discharge of battery cells 154, therefore,the accuracy of the timing signal is very important, as any inaccuraciesin the timing will affect the calculation of the amount ofself-discharge of battery cells 154.

[0031] Although good results have been achieved in the present inventionutilizing oscillator circuit 116 and crystal 150 to generate the timingsignal as described hereinabove, it is contemplated to be within thescope of this invention that other types of highly accurate, temperaturestable signal generators could be used, such as, but not by way oflimitation, the Dallas Semiconductor DS 1075, and other on-chip accuratenon-crystal oscillators, and laser trimmed, high accuracy oscillators.It is further contemplated that the timing signal generator could befrom another source, such as a microprocessor's clock in the batterypack.

[0032] As further depicted in FIG. 1, battery monitoring circuitry 102includes scratch pad memories 122-128. Scratchpad memories 122-128 helpto insure data integrity during communication of data over the one-wiredata bus. In operation, data is first written to the scratchpad memory,where it can be read back for verification. After the data has beenverified, the data will be transferred to the appropriate page inmemory. The process insures data integrity when modifying the contentsof the registers. As illustrated, each scratchpad memory contains acyclic redundancy check (CRC) byte, which is the CRC over all of thebytes in a currently selected scratchpad memory. The CRC is used tovalidate the communication.

[0033] Referring now to FIG. 2, there is illustrated a graph 200representing the activity of ICA 142, CCA 144, and DCA 146 over a samplecharge/discharge cycle of battery cells 154. As depicted, line 210represents the activity of ICA 142, line 212 represents the activity ofCCA 144, and line 214 represents the activity of DCA 146. During timeperiod t₁, the first charging period 216, the values of ICA 142 and CCA144 are increasing as the current flow into the rechargeable battery ispositive while DCA 146 remains inactive. However, during time periods t₃and t₄, discharge periods 218 and 220, the value of ICA 142 decreasesand the value of DCA 146 increases as the current flows out of therechargeable battery while the value of CCA 144 remains unchanged.During time period t₆, the second charging period 222, the values of ICA142 and CCA 144 again increase, while the value of DCA 146 remainsunchanged. As is evident from graph 200, when battery cells 154 becomefully discharged and current stops flowing out of the battery cells 154,the values of CCA 144 and DCA 146 are maintained, while the value of ICA142 will be at or near a count of zero.

[0034] As can be appreciated, the accuracy of the clock signal drivingICA, CCA and DCA is very important. Any error that occurs in the clocksignal will be directly reflected in accumulators 142, 144 and 146 andthereby give a less accurate reading as to the remaining charge ofbattery cells 154.

[0035] Although the present invention is illustrated in relationshipwith a rechargeable battery system, it is contemplated that the presentinvention could also be utilized in non-battery applications, as well asnon-electrical applications. For example, in a system where the life ofthe system is base upon the current flowing into the device, such as anelectric motor, the present invention could be utilized to monitor thecurrent flowing into the system and used to determine the remainingoperating life thereof.

[0036] It can be further appreciated that the present invention providesa method using electronic circuitry for monitoring and accumulatingvarious operating parameters of a rechargeable battery with selectedparameters being used to determine the remaining operating life of arechargeable battery. The circuitry includes a current monitor formeasuring the current flow into and out of the rechargeable battery. Anintegrated current accumulator, connected to the current monitor, isused to maintain a net accumulated total of current flowing into and outof the rechargeable battery. A charging current accumulator, which isalso coupled to the current meter is used to maintain the total currentflowing into the rechargeable battery, while a discharging currentaccumulator is used to maintain the total current flowing out of therechargeable battery. An oscillator circuit is used to time each of theaccumulators to assure high accuracy of the gas gauge calculationstherefrom.

[0037] Although a preferred embodiment of the present invention has beenillustrated in the accompanying Drawings and described in the foregoingDetailed Description, it will be understood that the invention is notlimited to the embodiment disclosed, but is capable of numerousrearrangements, modifications and substitutions without departing fromthe spirit of the invention as set forth and defined by the followingclaims.

What is claimed is:
 1. A method for monitoring at least one parameterassociated with a rechargeable power supply, said method comprising thesteps of: generating a timing signal with a timekeeper; and monitoringthe at least one parameter associated with the rechargeable power supplyat select intervals timed by said timing signal.
 2. The method asrecited in claim 1 , wherein said step of monitoring the at least oneparameter includes measuring, with a current monitor, at leastindications of discharging current from the rechargeable power supply.3. The method as recited in claim 1 , and further comprising the step ofaccumulating, with a first accumulator, values representing the totalamount of charge having flowed out of the rechargeable power supply. 4.The method as recited in claim 2 , and further comprising the step ofmeasuring, with the current monitor, at least indications of chargingcurrent into the rechargeable power supply.
 5. The method as recited inclaim 4 , and further comprising the step of accumulating, with a secondaccumulator, values representing the total amount of charge havingflowed into the rechargeable power supply.
 6. The method as recited inclaim 4 , and further comprising the step of accumulating, with a thirdaccumulator, values representing the net amount of charge having flowedinto and out of the rechargeable power supply.
 7. The method as recitedin claim 1 , wherein said step of monitoring the at least one parameterincludes monitoring, with a temperature monitor, the temperature of therechargeable power supply.
 8. The method as recited in claim 1 , andfurther comprising the step of generating an end-of-charge timestamp inresponse to the completion of the charging of the rechargeable powersupply.
 9. The method as recited in claim 1 , and further comprising thestep of generating a disconnect timestamp.
 10. The method as recited inclaim 9 , and further comprising the step of calculating the amount ofself-discharge of the rechargeable power supply based upon thedisconnect timestamp.
 11. A method for monitoring at least on parameterassociated with a rechargeable power supply, said method comprising thesteps of: generating a timing signal with a timekeeper; measuring, witha current monitor, the current flow out of the rechargeable power supplyat select time intervals timed by the timing signal; and measuring, withthe current monitor, the current flow into the rechargeable power supplyat select time intervals timed by the timing signal.
 12. The method asrecited in claim 11 , and further comprising the step of monitoring,with a temperature monitor, the temperature of the rechargeable powersupply at select time intervals timed by the timing signal.
 13. Themethod as recited in claim 11 , as further comprising the step ofmonitoring, with a voltage monitor, the potential level of therechargeable power supply.
 14. The method as recited in claim 11 , andfurther comprising the steps of: accumulating the net total current flowinto the rechargeable power supply; and accumulating the net total ofcurrent flow out of the rechargeable power supply.
 15. The method asrecited in claim 12 , and further comprising the step of generating asignal corresponding to the temperature measured during said step ofmonitoring the temperature of the rechargeable power supply.
 16. Themethod as recited in claim 12 , and further comprising the step ofmonitoring, with a voltage monitor, the potential level of therechargeable power supply.
 17. The method as recited in claim 16 , andfurther comprising the steps of: accumulating the net total of currentflow into the rechargeable power supply; and accumulating the net totalof current flow out of the rechargeable power supply.
 18. The method asrecited in claim 17 , and further comprising the step of generating asignal corresponding to the temperature measured during said step ofmonitoring of the temperature of rechargeable power supply.
 19. Themethod as recited in claim 18 , and further comprising the step ofstoring data corresponding to the signal generated in said step ofgenerating a signal corresponding to the temperature measured.
 20. Themethod as recited in claim 19 , and further comprising the step ofgenerating an end-of-charge timestamp in response to the completion ofthe charging of the rechargeable power supply.
 21. The method as recitedin claim 20 , and further comprising the step of generating a disconnecttimestamp in response to the disconnect of the rechargeable power supplyfrom a system.
 22. The method as recited in claim 21 , wherein thetimekeeper used in said step of generating clock signals includes anoscillator circuit.
 23. The method as recited in claim 22 , wherein thetimekeeper is connectable to a crystal.
 24. The method as recited inclaim 23 , wherein the voltage monitor, used in said step of monitoringthe potential level of the rechargeable power supply, includes ananalog-to-digital converter.
 25. The method as recited in claim 24 ,wherein the current monitor, used in said step measuring the currentflow into the rechargeable power supply at select time intervals,includes an analog-to-digital converter.
 26. A method for monitoringparameters associated with a rechargeable battery, said methodcomprising the steps of: generating, with an oscillatory circuit, atiming signal; monitoring, with a temperature sensor, the temperature ofthe rechargeable battery at select time intervals time by the timingsignal; measuring, with a voltage meter coupled to the rechargeablebattery, at least an indication of the potential level of therechargeable battery at select time intervals timed by the timingsignal; measuring, with a current meter coupled to the rechargeablebattery, at least indications of current flow into and out of therechargeable battery at select time intervals timed by the timingsignal; accumulating, with an accumulator coupled to the current meter,the net total of current flow into the rechargeable battery and the nettotal of current flow out of the rechargeable battery.